This invention relates generally to magnetic disk drives, more particularly to magnetoresistive (MR) read heads, and most particularly to methods and structures for current-perpendicular-to-plane (CPP) operation of submicron GMR heads.
Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk drive 10 of the prior art includes a sealed enclosure 12, a disk drive motor 14, a magnetic disk 16, supported for rotation by a drive spindle SI of motor 14, an actuator 18 and an arm 20 attached to an actuator spindle S2 of actuator 18. A suspension 22 is coupled at one end to the arm 20, and at its other end to a read/write head or transducer 24. The transducer 24 typically includes an inductive write element with a sensor read element (shown in FIG. 1C). As the motor 14 rotates the magnetic disk 16, as indicated by the arrow R, an air bearing is formed under the transducer 24 causing it to lift slightly off of the surface of the magnetic disk 16, or, as it is termed in the art, to "fly" above the magnetic disk 16. Various magnetic "tracks" of information can be read from the magnetic disk 16 as the actuator 18 causes the transducer 24 to pivot in a short arc as indicated by the arrows P. The design and manufacture of magnetic disk drives is well known to those skilled in the art
FIG. 1C depicts a magnetic read/write head 30 including a read element 32 and a write element 34. The edges of the read element 32 and write element 34 also define an air bearing surface ABS, in a plane 33, which faces the surface of the magnetic disk 16.
Read element 32 includes a first shield 36, a second shield 38, and a read sensor 40 that is located between the first shield 36 and the second shield 38. One type of read sensor 40 is a magnetoresistive (MR) sensor which can be a variety of types, such as anisotropic magnetoresistive (AMR), spin valve, and giant magneto-resistive (GMR). The particular read sensor 40 shown is a multilayer GMR, formed of successive layer pairs 42 of various materials. Such an MR device typically can be formed by depositing the layer pairs 42 one upon the next to form a multilayer wafer (not shown). The material of each layer and the ordering of layers are appropriately selected to achieve a desired read performance. Multiple portions of the wafer are then removed to provide multiple read sensors 40.
Write element 34 of FIG. 1C is typically an inductive write element and includes a first yoke element 44 and the second shield 38, which forms a second yoke element, defining a write gap 46 therebetween. The first yoke element 44 and second yoke element 38 are configured and arranged relative to each other such that the write gap 46 has a particular throat height, TH. Also included in write element 34, is a conductive coil 48 that is positioned within a dielectric medium 50. As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk 16.
The operation of the read element 32 can be better understood with reference to the cross-sectional view of read element 32 in FIG. 1D. A sense current I is caused to flow 15 through the read sensor 40. While in FIG. 1D the sense current is shown injected through the shields (which act as leads), in other configurations the read sensor electrically isolated from the shields, with additional leads injecting the sense current I. Specifically, FIG. 1D depicts a four-point configuration, where a lead lies between each shield and the read sensor. In such a configuration, the sense current I passes through the first shield 36, through a first sense lead 37, then through the read sensor 40 to a second sense lead 39 and to the second shield 38. As the sense current I passes through, the read sensor exhibits a resistive response, resulting in an output voltage that can be quantified by measuring the voltage drop across the two sense leads 37, 39. The higher the output voltage, the greater the precision and sensitivity of the read sensor in sensing magnetic fields from the magnetic medium 16.
The output voltage is affected by various characteristics of the read element 32. For example, the greater the component of a sense current that flows perpendicular to the read sensor layers, as indicated by the vector CPP, the greater the output voltage. This component of sense current is the current-perpendicular-to-plane, CPP, component. For example, the sense current I of FIG. 1D is CPP. On the other hand, the component of a sense current that flows along (or parallel to) the read sensor layers 42 is the current-in-plane, CIP, component. Such current would occur in the read sensor 40 of FIG. 1D perpendicular to the sense current I either parallel to, as indicated by the vector CIP, or through the plane of the view.
In the configuration of FIG. 1D, the first and second shields 36, 38 are conductive and are in electrical contact with the read sensor 40. Here, the sense current I of the read sensor 40 flows, for example, from the first shield 36 to the second shield 38 through the read sensor 40. As the sense current I flows through the read sensor 40, the current flows substantially perpendicularly to the orientation of the layers 42 of the read sensor 40. Thus, substantially all of the sense current I is CPP, i.e., the read sensor 40 operates in CPP mode. Other read sensors may be designed to operate with varying CPP and CIP components of the sense current. However, it is desirable to maximize the CPP component to maximize the output voltage of the read sensor. The design and manufacture of such magnetoresistive heads, such as read sensor 40, are well known to those skilled in the art.
Although current GMR read sensors such as read sensor 40 have been used in the past, their performance is limited. In particular, various aspects of the read sensor fabrication can result in undesirable edge circuit paths between edges E of the read sensor layers. For example, as is shown in FIG. 1E, if etching is performed on multiple layers in the same operation, there can be redeposition 43 of the etched material of one layer upon the etched edge of another layer. Also, during lapping of the read sensor to form the air bearing surface ABS, or during a cutting operation to remove a single read sensor from a wafer, material can be smeared from one layer to another layer. In addition, when the read sensor layers are exposed to high temperatures diffusion might occur between the layers. When particular redeposition, smearing, or diffusion occurs between conductive layers, circuit paths can be formed between those layers at their edges E. Additionally, while such circuit paths can be formed between layers of a variety of types of read sensors, the problem can be more extensive or more likely in read sensors which have layers of smaller thicknesses, for example GMR sensors.
When such circuit paths are formed, the sense current I can be disrupted, as is illustrated by the charge flow lines 44 of FIG. 1E. The charge, illustrated by charge flow lines 44a, that flows through the sensor in a region away from the edges E, the edge-free sensor portion 46, is substantially unaffected by the edge circuit paths and is primarily in CPP mode. However, the charge, illustrated by charge flow lines 44b and 44c, that flows through the sensor in a region nearer to the edges E, the edge sensor portion 48, can be shunted away from a direct path between the first shield 36 and the second shield 38. Such shunting reduces the sensitivity of the device because current is directed away from and around the multilayer. The shunted portion of the current does not typically exhibit any MR or GMR effect because an edge circuit path is typically an unstructured mixture of materials that have been re-sputtered or re-deposited from the etched portion of the device. This phenomenon is sometimes referred to as an edge effect While it may be possible to remove the material along the edges E, it would be technically very difficult and may have undesirable side effects. For example, such a process would likely change the dimensions of the read sensor, because the etching technique used will not be able to differentiate between the redeposited material and the sensor itself Also, the process would necessarily result in the removal of other portions of the device, such as the leads. Furthermore, with increasingly dense media being used to provide more data, and the need for correspondingly smaller read devices, read sensors will have larger edge-to-volume ratios which can be expected to increase the impact of the edge effect on read sensor performance.
Thus, what is desired is a GMR head, and a method for making the same, that can operate in CPP mode with increased performance despite the existence of edge circuit paths, while limiting cost and complexity.